Hitachi TrueCopy for z/OS (T1711-96009, June 2006)

30 TrueCopy for the XP1024/XP128/XP12000/XP10000
TrueCopy Asynchronous Recordset Operations
The TC390A recordsets contain the TC390A M-VOL updates and the associated control information,
including the time-stamp of the M-VOL update, which enables the RCU to maintain update consistency of
the TC390A R-VOLs. TC390A recordset operations include:
• Creating and storing recordsets at the MCU
• Sending recordsets to the RCU
• Storing recordsets at the RCU
• Selecting and settling recordsets at the RCU
• Types of recordsets
• Inflow control for sidefiles
Creating and Storing Recordsets at the MCU
When an MCU performs an update (host-requested write I/O) on a TC390A M-VOL, the MCU creates a
TC390A recordset that contains: the updated record, time-stamp information, sequence number, record
location (device, cylinder, track, record number), and record length. The TC390A recordsets are queued in
the cache storage of the MCU and sent to the RCU independent of host I/O processes. The RCU uses the
time-stamp and sequence number information in the recordsets to update the R-VOL(s) in the same order as
the M-VOL(s).
The time-stamp information is acquired from the (MVS) host’s I/O time-stamp function. This time stamp
provides a protective measure for write-dependent applications and minimizes recovery time in the event of
a disaster. The sequence number indicates the number of recordsets that the MCU has created for each
consistency group. The recordset information, except for the updated records, is stored and queued in an
area of cache known as sidefile cache. For more information on sidefile cache, see
”Inflow Control of
Recordsets” on page 32
.
Sending Recordsets to the RCU
The MCU sends the TC390A recordsets to the RCU in a similar manner to the TC390 Synchronous
updates. The MCU’s RCPs and/or initiator ports act as host processor channels and issue special I/O
operations, called remote I/Os (RIOs), to the RCU. The RIO transfers the recordsets in FBA format (not
CKD) using a single channel command, eliminating the overhead associated with FBA-CKD conversion
and thus providing more efficient transfer of user data. The MCU can send several recordsets using a single
RIO, even if their sequence numbers are not contiguous. Therefore, TC390A recordsets are usually sent to
the RCU in a different order than the arrivals at the MCU. The RCU ensures that records are applied to the
R-VOLs in the correct sequence. This method of remote I/O provides the most efficient use of MCU-to-RCU
link resources.
3380-3 3,339 1 11,605 16,384
3390-1 1,113 1 11,605 16,384
3390-2 2,226 1 11,605 16,384
3390-3
3390-3R
3,339 1 11,605 16,384
3390-9 10,017 2 5,802 14,335
3390-L 32,760 5 2,321 5,734
3390-M 65,520 9 1,289 3,185
Table 7 Maximum Number of Pairs According to Each Emulation Type, when pairs are created without
use of customized volume
Emulation
Type
Number of
Cylinders
Number of
Bitmap Areas
Maximum Number of Pairs
(Added Shared Memory:
1 set)
Maximum Number of Pairs
(Added Shared Memory:
2 sets)